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SubjectRe: cgroup: deadlock between cpu_hotplug_lock and freezer_mutex
From
Hi Hillf,

On 15/02/2023 15:25, Hillf Danton wrote:
> On Wed, 15 Feb 2023 10:07:23 +0800 Xiubo Li <xiubli@redhat.com>
>> Hi
>>
>> Recently when running some test cases for ceph we hit the following
>> deadlock issue in cgroup code. Has this been fixed ? I have checked the
>> latest code and it seems no any commit is fixing this.
>>
>> This call trace could also be found in
>> https://tracker.ceph.com/issues/58564#note-4, which is more friendly to
>> read.
>>
>>  ======================================================
>>  WARNING: possible circular locking dependency detected
>>  6.1.0-rc5-ceph-gc90f64b588ff #1 Tainted: G S
>>  ------------------------------------------------------
>>  runc/90769 is trying to acquire lock:
>>  ffffffff82664cb0 (cpu_hotplug_lock){++++}-{0:0}, at:
>> static_key_slow_inc+0xe/0x20
>>  #012but task is already holding lock:
>>  ffffffff8276e468 (freezer_mutex){+.+.}-{3:3}, at: freezer_write+0x89/0x530
>>  #012which lock already depends on the new lock.
>>  #012the existing dependency chain (in reverse order) is:
>>  #012-> #2 (freezer_mutex){+.+.}-{3:3}:
>>        __mutex_lock+0x9c/0xf20
>>        freezer_attach+0x2c/0xf0
>>        cgroup_migrate_execute+0x3f3/0x4c0
>>        cgroup_attach_task+0x22e/0x3e0
>>        __cgroup1_procs_write.constprop.12+0xfb/0x140
>>        cgroup_file_write+0x91/0x230
>>        kernfs_fop_write_iter+0x137/0x1d0
>>        vfs_write+0x344/0x4d0
>>        ksys_write+0x5c/0xd0
>>        do_syscall_64+0x34/0x80
>>        entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>  #012-> #1 (cgroup_threadgroup_rwsem){++++}-{0:0}:
>>        percpu_down_write+0x45/0x2c0
>>        cgroup_procs_write_start+0x84/0x270
>>        __cgroup1_procs_write.constprop.12+0x57/0x140
>>        cgroup_file_write+0x91/0x230
>>        kernfs_fop_write_iter+0x137/0x1d0
>>        vfs_write+0x344/0x4d0
>>        ksys_write+0x5c/0xd0
>>        do_syscall_64+0x34/0x80
>>        entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>  #012-> #0 (cpu_hotplug_lock){++++}-{0:0}:
>>        __lock_acquire+0x103f/0x1de0
>>        lock_acquire+0xd4/0x2f0
>>        cpus_read_lock+0x3c/0xd0
>>        static_key_slow_inc+0xe/0x20
>>        freezer_apply_state+0x98/0xb0
>>        freezer_write+0x307/0x530
>>        cgroup_file_write+0x91/0x230
>>        kernfs_fop_write_iter+0x137/0x1d0
>>        vfs_write+0x344/0x4d0
>>        ksys_write+0x5c/0xd0
>>        do_syscall_64+0x34/0x80
>>        entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>  #012other info that might help us debug this:
>>  Chain exists of:#012  cpu_hotplug_lock --> cgroup_threadgroup_rwsem
>> --> freezer_mutex
>>  Possible unsafe locking scenario:
>>        CPU0                    CPU1
>>        ----                    ----
>>   lock(freezer_mutex);
>>                                lock(cgroup_threadgroup_rwsem);
>>                                lock(freezer_mutex);
>>   lock(cpu_hotplug_lock);
>>  #012 *** DEADLOCK ***
> Thanks for your report.
>
> Change locking order if it is impossible to update freezer_active in atomic manner.
>
> Only for thoughts.

Sure, I will test this.

Thanks


>
> Hillf
> +++ linux-6.1.3/kernel/cgroup/legacy_freezer.c
> @@ -350,7 +350,7 @@ static void freezer_apply_state(struct f
>
> if (freeze) {
> if (!(freezer->state & CGROUP_FREEZING))
> - static_branch_inc(&freezer_active);
> + static_branch_inc_cpuslocked(&freezer_active);
> freezer->state |= state;
> freeze_cgroup(freezer);
> } else {
> @@ -361,7 +361,7 @@ static void freezer_apply_state(struct f
> if (!(freezer->state & CGROUP_FREEZING)) {
> freezer->state &= ~CGROUP_FROZEN;
> if (was_freezing)
> - static_branch_dec(&freezer_active);
> + static_branch_dec_cpuslocked(&freezer_active);
> unfreeze_cgroup(freezer);
> }
> }
> @@ -379,6 +379,7 @@ static void freezer_change_state(struct
> {
> struct cgroup_subsys_state *pos;
>
> + cpus_read_lock();
> /*
> * Update all its descendants in pre-order traversal. Each
> * descendant will try to inherit its parent's FREEZING state as
> @@ -407,6 +408,7 @@ static void freezer_change_state(struct
> }
> rcu_read_unlock();
> mutex_unlock(&freezer_mutex);
> + cpus_read_unlock();
> }
>
> static ssize_t freezer_write(struct kernfs_open_file *of,
>
--
Best Regards,

Xiubo Li (李秀波)

Email: xiubli@redhat.com/xiubli@ibm.com
Slack: @Xiubo Li

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